In a room or space called a data center, a machine room or a server room, Information Technology (IT) devices such as servers, and a rack on which IT devices are stacked and mounted are placed.
An IT device has functional components such as the Central Processing Unit (CPU), the memory, and the like, and the functional components fulfill their functions while consuming power. Then, heat is generated as a result, but in order to guarantee the operation, or in order to secure the reliability of the operation, the temperature of functional components need to be kept equal to or below a certain temperature. For this reason, IT devices generally have an airflow generation component, for cooling by forced air cooling and the like.
For a general IT device, on an assumption that air of a temperature equal to or below a certain temperature is taken in from an air intake, the upper limit temperature of the air to be taken is determined as the operation guarantee temperature. In a data center and a machine room, a number of IT devices are placed in a certain space/room, and if no measure is taken, the temperature of the air in the space/room keeps increasing by heat generation by the IT devices.
Then, in a data center and a machine room in which IT devices are placed, generally, in the same space/room or in a separately-provided room, space, an air conditioning system that has a function to draw heat from the IT device installation area and to release it outside the area in which the IT devices are placed is provided so that the operation guarantee temperature of the IT devices is not exceeded.
Therefore, in the air circulation of the space/room, the reasonable form is that the air of a relatively row temperature released from the air conditioning system is provided to the air intake plane of the IT devices/IT device mounting rack, and the airflow generation component such as a fan built in the IT device is driven to take it in, thereby cooling the functional components such as the CPU, and the air of a relatively high temperature that has drawn the heat of the IT device is released from the IT device's outlet. The air promptly returns to the intake of the air conditioning system, and is taken in into the air conditioner, where its heat is drawn and it becomes air of a low temperature, and is blown out of the air conditioner.
In a general data center, IT devices are placed in the center part of the computer room, and the air conditioner is placed in the peripheral area of the computer room. In some cases, it is placed outside the computer room in which IT devices are placed, and as a result, it may be placed in the surroundings of the IT device installation area. In this case, the air conditioner is in charge of cooling IT devices in a broad area, and performing generally-even cooling.
However, in a data center, if heat generation density of the IT devices is not even and heat generation is concentrated locally, the airflow required by the IT devices also increases locally, and an air conditioner that provides evenly-cold air can no longer provide the required air volume. When supply of cold air falls short, the exhaust of the IT devices comes around to the intake plane side, making an area where the intake temperature of the IT device is high. The reliability of an IT device generally decreases when its intake temperature becomes high, and its life is also shortened.
As a method for solving this problem, additional installment of an air conditioner placed in the outer circumference of the computer room would be possible, but it is difficult to deliver the effect to a specific place, and energy will be wasted as the effect extends into a broad area and useless cooling will be performed for the part that does not require additional cooling power.
As another solution, there is a method in which a local air conditioner is installed in the vicinity of an IT device that has a high heat generation density. Since installment can be made in the vicinity of the area with local heat generation, the efficiency may be improved.
In data centers in recent years, the intake area and the exhaust area are often separated. By doing so, cold air released from the air conditioner is provided to the intake plane of the IT device, to avoid exhaust of a high temperature from coming around to the IT device intake plane to improve the reliability of the IT device, and the exhaust of the IT device is returned to the air conditioner while keeping it at the high temperature, to improve the efficiency of the air conditioner.
In the viewpoint of safe operation, it is important to measure and manage the intake temperature and the exhaust temperature of the IT devices in a data center. Especially in a data center, a number of IT devices are aligned and installed and a wide area is managed collectively, the temperature distribution in a wide area needs to be measured efficiently.
In the conventional intake/exhaust temperature management method, a temperature sensor such as a thermistor and the like that obtains temperature information from an electric signal is placed on the intake plane or the exhaust plane of the rack. With this method, however, there has been a problem that a large number of sensors need to be prepared and installed to capture temperature distribution in a wide area, especially temperature distribution in the wide area in which a plurality of IT devices are aligned and installed, which is troublesome.    [Patent document 1] Japanese Laid-open Patent Publication No. H11-6770    [Patent document 2] Japanese Laid-open Patent Publication No. 2000-323883    [Patent document 3] Japanese Laid-open Patent Publication No. 2002-118387    [Patent document 4] Japanese Laid-open Patent Publication No. H11-83643